Closed-loop digital control of an impact printer hammer

This paper explores closed-loop digital control of a high-speed impact printer hammer in the presence of sensor measurement noise and disturbances. Conventional control of high-speed impact printers is accomplished without feedback; hence disturbances, such as mechanical and magnetic interaction between hammers and hammer settle-out period, force long delays between hammer firings to assure proper time and velocity of impact. By computer simulation, we show the feasibility of using the solenoid actuator to control both time and velocity of impact. This is accomplished by setting an initial trajectory and introducing mid-course guidance based on state estimates derived from hammer position measurements and a Kalman filter estimator. To overcome difficulties in performing necessary computations in a short time, and in synchronizing the digital system to the “real world,” the controller allows the solenoid to be commanded “on and “off between samples. Although the solenoid actuator produces a force in one direction only, the same control law is used to decelerate the hammer on the return trip, bringing it to a soft landing that provides satisfactory initial conditions for the next hammer command. Attention isgiven to computation time required, and a general scenario for real-time implementation is given.